In recent times the use of modern composite materials is becoming increasingly widespread. However, the failure modes of composite structures are extremely complex and, unlike metals, they may suffer significant degradation with barely visible surface damage. Since the damage may cause serious decrease in material strength and lead to catastrophic failure, the development of reliable structural health monitoring (SHM) techniques can have a tremendous impact on the life-cycle cost spent for inspection and repair.
As a result, a number of nondestructive evaluation techniques have been put forward, including dielectric spectroscopy, ultrasonic evaluation, vibration analysis, phased array analysis, shearography, thermography, infrared thermography, ultrasonic phased array, sampling phased array (SPA), synthetic aperture focusing technique (SAFT), flash thermography, dynamic modulus measurements, and acoustic emission monitoring.